The embodiments described herein relate generally to hybrid power plant systems, and more particularly, to methods and systems of distributing active power sourcing in hybrid power plant systems.
In certain hybrid power plant systems, a synchronous generator shares production of power demanded by a load with other sources of power to drive an engine. The other sources of power are often of a direct current (DC) nature, for example, a battery bank coupled in parallel with the generator. The hybrid power plant systems are generally those that have variable power demand are designed such that no single power source is capable of providing all the required power during periods of high power demand.
In such hybrid systems, the generator includes a voltage regulator for output voltage by the generator. A typical voltage regulator has a function that lets a user define a desired generator output voltage. The voltage regulator measures the generator's output voltage and attempts to keep it at that user-defined voltage by increasing or decreasing excitation current to the generator. Typical voltage regulators tend to have problems in sharing the load demand with the battery bank. Because the battery bank is not an ideal and constant DC power source, it outputs a voltage which is dependent on charging and/or discharging conditions at a particular instant in time. If the voltage of the battery bank is lower than the rectified generator output voltage, the battery bank suppresses the generator output voltage. Conversely, if the voltage of the battery bank is higher than the rectified generator output voltage, the battery bank unloads the generator, causing the generator output voltage to increase. Because of the influence of the battery voltage on the generator output voltage, the voltage regulator continuously reacts to changes in battery voltage, which may cause unstable voltages regulation and/or other conditions that may trip faults, which may cause nuisance behavior and/or damage or destroy system components. Such poor load sharing is due to the voltage regulator's response to battery loading characteristics. Known methods of load sharing do not alter the voltage regulator's control strategy during periods of battery draw.
For example, in a hybrid vehicle with an engine-generator set and a battery bank, during normal operation, the generator alone provides sufficient power for the electric motors to enable the vehicle to move. But, if the vehicle is driven up a steep hill, or if the load is increased, the generator may need assistance from the battery bank for short durations. The voltage regulator on the vehicle must recognize a heavy load condition and control the generator output to achieve load sharing with the batteries. Voltage regulators that are not designed for load sharing with DC sources provide poor load sharing during engagement of battery power draw because they are constantly reacting to influences of instantaneous changes in battery terminal voltage. Voltage regulators that do not implement a strategy for battery load sharing exhibit unsteady voltage regulation, causing periods of engine overloading. This may cause the engine speed to drop during the overload event, further causing a voltage dip to ripple through the electrical drive system. Voltage dips may cause nuisance power trips of downstream connected power converters and may cause the vehicle to lose power.